The present invention relates generally to optical head devices used in disc players and to methods for making thermally-conductive casings or covers for such optical heads. Particularly, the casings for the optical heads are made from polymer compositions comprising a base polymer matrix and a thermally-conductive material.
Today, optical recording media, such as compact discs (CDs) and digital video discs (DVDs), are widely used to record and playback information including music, photos, movies, and the like. In general, the surface of an optical disc contains minute recesses or pits corresponding to the recorded information. An optical head device reads the information on the optical disc, and the information is played back accordingly.
In general, the optical head device emits a laser light beam, directs and focuses the light beam onto the optical disc so as to generate reflected light from the disc, and guides the reflected light to photodetectors. The amount of reflected light generated by the optical disc changes due to the varying depths and structures of the minute pits on the surface of the disc. The recorded information on the optical disc is played back in accordance with the changes in reflected light from the disc.
Conventional optical head devices comprise various optical components that are assembled within a hard casing or covering. Typically, the components include a semiconductor laser for generating a laser light beam, an objective lens for focusing the laser beam onto the optical disc, and a focus/track signal detection element for maintaining the light beam in correct focus so that there are no tracking errors. The optical head includes various other lenses, mirrors, filtering prisms, photodetector elements, and the like. The industry continues to develop new optical head designs.
For example, Mitsumori et al., U.S. Pat. No. 5,005,162 discloses an optical head device for use in a disc player comprising a movable optical assembly in which an objective lens, first and second mirrors, and a light beam-generating/ detecting unit are supported in common by a supporting member.
Lee et al., U.S. Pat. No. 6,078,555 discloses different optical head assemblies having compatibility -with a recordable compact disc (CD-R) and a digital video disc (DVD). The Pat.discloses a conventional assembly containing a first light source for emitting a first light beam having a wavelength of 635 nm for recording and reproducing information with respect to a DVD. The assembly also includes a second light source for emitting a second light beam having a wavelength of 780 nm for recording and reproducing information with respect to a CD-R. The Patent further describes an optical head assembly having a stationary first optical unit and a movable second optical unit. The second optical unit moves at a high speed on a guide rail which is installed along the diameter direction of the DVD or CD-R. The first optical unit emits a first light beam to the second optical unit and detects information from the first light beam reflected from the loaded optical disc and received by the second optical unit. The second optical unit focuses the first light beam and can generate a second light beam on the loaded optical disc depending on the type of optical disc (DVD or CD-R).
Shiono et al., U.S. Pat. No. 6,487,016 discloses a method for making a thinner optical head. The optical head comprises a light path alteration member, a first grating element, and a second grating element arranged in a light path between a light source and an optical disc.
The optical heads can generate a substantial amount of heat during operation, and the heat must be removed in order for the device to function properly. The industry has attempted to address this problem in a variety of ways.
Nagano, U.S. Pat. No. 5,680,385 discloses an optical head comprising a laser diode chip; a lens which focuses emitted light on an optical disc; a diffraction element which diffracts reflected light from the optical disc; and light detecting portions which convert the diffracted lights into electrical signals. The laser diode is fixed to a heat sink. The Patent discloses that the heat sink can be made of a semiconductor such as silicon, orientation-selective (anisotropic) etching, casted metal, or ceramic.
In other instances, the components of the optical head are contained within a metallic casing which dissipates the heat. The casing can be made from aluminum, copper, zinc, and other metals. For instance, a sheet of aluminum can be milled or cast into a desired shape for the casing. Although a metallic casing can dissipate a substantial amount of heat, it has several drawbacks. The metallic casing tends to have a heavy weight. Further, the process for manufacturing a metallic casing can be time-consuming and costly. Also, it can be cumbersome to produce casings having complex shapes using metal stamping, casting, or milling processes.
It is also common to make optical head casings using conventional plastic compositions. These known plastic compositions have some benefits. For example, the plastics can be injection-molded to produce the optical head casing. Plastic casings tend to have a lightweight construction. However, these traditional plastic casings have generally poor thermal conductive properties. Thus, metal heat spreaders or other similar parts must be installed for transferring and dissipating the heat. The addition of metallic parts to the optical head assembly adds an additional step to the manufacturing of the head and can be costly.
In view of the foregoing problems, it would be desirable to have a method for making a thermally-conductive, plastic casing for an optical head, wherein the casing has sufficient thermal conductivity, and it is not necessary to add metal heat spreaders or other heat management parts to the assembly. The present invention provides such a method.
This invention relates to relates to a method for making a molded casing or covering for an optical head device using thermally-conductive polymer compositions. The optical head device, having a thermally-conductive casing in accordance with the present invention, can be used in optical disc players such as CD and/or DVD players.
The thermally-conductive polymer composition comprises: a) 20% to 80% by weight of a polymer matrix, and b) 20% to 80% by weight of a thermally-conductive, filler material. The polymer composition may further comprise 3% to 50% by weight of a reinforcing material. The polymer matrix can be a thermoplastic or thermosetting polymer. For example, polyphenylene sulfide can be used to form the polymer matrix. The thermally-conductive, filler can be a metal, metal oxide, ceramic, carbon or other suitable material. For example, the thermally-conductive filler can be selected from the group consisting of aluminum, copper, magnesium, brass, alumina, silicon oxide, boron nitride, silicon nitride, carbon black, or carbon graphite. The reinforcing material can be glass, inorganic minerals, or other suitable mechanical strengthening agent. The polymer composition may further contain additives such as, for example, flame retardants, antioxidants, plasticizers, dispersing aids, and mold-releasing agents.
A molten polymer composition is provided, and the composition is injected into a mold. The composition is then removed from the mold to form a net-shape molded, thermally-conductive casing for an optical head device.
Preferably, the shaped article (casing) has a thermal conductivity of greater than 3 W/mxc2x0 K., and more preferably greater than 22 W/mxc2x0 K.